► The primary motivation of this work is to simulate the complex behavior of oil, gas and water as it flows through an unconventional reservoir. Unconventional…
(more)

▼ The primary motivation of this work is to simulate the complex behavior of oil,
gas and water as it flows through an unconventional reservoir. Unconventional reservoirs require hydraulic fracturing to provide the reservoir with conductive pathways for fluid to flow. Without fracturing the rock, the oil and gas would remain trapped in impermeable pore spaces. Unconventional reservoirs typically exhibit high heterogeneity in rock properties but also in fluid flow regimes. A simulation tool needs to be able to capture small scale rock heterogeneities, multiple flow regimes, and additional interaction physics between the rock and fluid.
In this dissertation, an alternative approach to modeling oil and gas reservoirs
at the field scale is presented. Instead of a ?top down? paradigm, typical of classic reservoir simulation techniques (finite element, finite volume and finite difference methods), this work focuses on a ?bottom up? paradigm called the latticeBoltzmann method (LBM).
The LBM is a numerical discretization of the Boltzmann equation, in which a
fluid is described as a distribution of particles, each with a unique velocity. The
evolution of the distribution of particles is governed by a series of streaming and collision operations. The streaming operation translates the particle distribution through space. The collision operator describes how the particle distribution interacts with other distributions – through collision and a transfer of momentum. The collective behavior of small scale particle dynamics (streaming and collision steps) yield macroscopic fluid behavior in the large space and time scale limit.
Advisors/Committee Members: Nasrabadi, Hadi (advisor), Gildin, Eduardo (committee member), Barrufet , Maria (committee member), King, Michael (committee member).

► In this study, the applicability of the LatticeBoltzmann Method to neutron transport is investigated. The transport model used, is derived from the Boltzmann equation…
(more)

▼ In this study, the applicability of the LatticeBoltzmann Method to neutron transport is investigated.
The transport model used, is derived from the Boltzmann equation for neutral particles by inverting
the streaming operator and casting the integral transport equation into an operator form. From the
operator equation, an iterative solution to the transport problem is presented, with the first collision
source as the starting point for the iteration scheme. One of the main features of the method is the
simultaneous discretization of the phase space of the problem, whereby particles are restricted to
move on a lattice.
A full description of the discretization scheme is given along with the iterative procedure and
quadrature set used for the angular discretization. To mitigate lattice ray effects, an angular
refinement scheme is introduced to increase the angular coverage of the problem phase space.
The method is then applied to a model problem to investigate its applicability to neutron transport.
Three cases are considered where constant, linear and exponential interpolants are used to account
for the accumulation of flux due to the streaming of particles between nodes. The results obtained
are compared to a reference solution, that was calculated by using the MCNP code and to the values
calculated using a nodal SN method. Finally, areas of improvement are identified and possible
extensions to the algorithm are provided.

► Superhydrophobic surfaces have been shown reduce drag in laminar flows; however, in turbulent flows, the literature is divided with drag reductions between 0% and 70%…
(more)

▼ Superhydrophobic surfaces have been shown reduce drag in laminar flows; however, in turbulent flows, the literature is divided with drag reductions between 0% and 70% being achieved. With frictional drag accounting for over half of the resistance of most ships, a method of decreasing drag would result in both significant fuel savings, and a reduction in carbon dioxide emissions. In order to ascertain whether these surfaces can provide a reduction in drag in turbulent flows, experimental and detailed computational fluid dynamics studies have been undertaken. In addition to determining whether turbulent flow drag reduction is achievable, this work investigated both the mechanics and conditions under which the drag reduction occurs, and quantified the interaction between the hydrophobic surface and the turbulent multiphase flow.The experimental program aimed to determine if drag reduction in high Reynolds number flows were achievable. As part of the research, a test rig was designed and constructed that allowed measurement of skin friction drag whilst minimising the effects of pressure drag. A hydrophobic surface was compared to a smooth plate across a range of turbulent flow Reynolds numbers with no noticeable drag reductions shown. Further investigations into the reasons for the lack of drag reduction were then achieved using computational fluid dynamics.The latticeBoltzmann method was used to accurately simulate the interactions between air and water at a scale where surface tension dominates. A code featuring methods which include fractional propagation, a novel technique of mesh refinement, a multiphase model and pseudo direct numerical simulation of turbulence has been devised and implemented. Validation across a range of benchmark tests was performed and the code proven to produce accurate results. An optimisation process was also undertaken to maximise efficiency.This code was then used to simulate laminar, transitional and turbulent flows through a smooth walled channel, and over a series of roughened and hydrophobic surfaces.The results of this research have confirmed that drag reductions in laminar and transitional flows are achievable; however, at Reynolds numbers greater than Re_tau = 390, minimal benefit was found because the air layer against the surface was removed. The drag reduction effect has been shown to be dependent on the location of the free-surface, and the way in which it insulates the ridges and posts on the hydrophobic surface from the water. The geometry of the surface has also been shown to have an effect on both the overall drag and the ability of the surface to maintain the insulating air layer.
Advisors/Committee Members: Barber, Tracie, Mechanical & Manufacturing Engineering, Faculty of Engineering, UNSW, Rosengarten, Gary, RMIT, Helmore, Phillip, Mechanical & Manufacturing Engineering, Faculty of Engineering, UNSW.

Baglin, A. (2016). Investigation of Drag Reduction in Turbulent Flow using Superhydrophobic Surfaces. (Doctoral Dissertation). University of New South Wales. Retrieved from http://handle.unsw.edu.au/1959.4/55475 ; https://unsworks.unsw.edu.au/fapi/datastream/unsworks:37797/SOURCE01?view=true

Baglin A. Investigation of Drag Reduction in Turbulent Flow using Superhydrophobic Surfaces. [Doctoral Dissertation]. University of New South Wales; 2016. Available from: http://handle.unsw.edu.au/1959.4/55475 ; https://unsworks.unsw.edu.au/fapi/datastream/unsworks:37797/SOURCE01?view=true

► This bio-inspired research will focus on using the latticeBoltzmann method (LBM) to calculate the drag of rigid geometries that resemble a sailfish bill inside…
(more)

▼ This bio-inspired research will focus on using the latticeBoltzmann method (LBM) to calculate the drag of rigid geometries that resemble a sailfish bill inside a channel with low fluid speed and high viscosity. These 2D simulation results will compare the performance of these similar structures, each with the same area but slightly different shapes, thus shedding light on the aerodynamic properties of the sailfish-bill-like structures in viscous fluids. The LBM model will be established using the open source code on Palabos in C/C++ to create the simulation channel and the obstacle, as well as to capture the fluid behavior on a mesoscopic scale and convert mesoscopic variables to macroscopic ones for data visualization and comparison purposes.
Advisors/Committee Members: Schaefer, Laura A (advisor).

Owing to the trend to development sustainability, solar systems (solar collector, solar concentrator, etc.) Are integrating (and asked to integrate even more) intensively residences and industries. In this context, two-phase systems like heat pipe seem highly effective because of their high heat transport capabilities and their passive operation in collectors’ technology. In view of the complexity of the heat pipes with a porous structure in this kind of application,most of the existing systems on the market use thermosyphons. Thus, the growing need of reliable and more efficient thermal control solutions is increasing for such systems. This thesis work focuses on the performance characterization of heat pipes with porous structure used in solar applications. A numerical study has been performed to model and simulate the behavior of a typical heat pipe using the LatticeBoltzmann method. An experimental study has also been done to characterize the performance of three prototypes tested under different conditions (condenser temperature, heat input and inclination angle). The effects induced by several parameters including the filling rate, working fluid and symmetry of the applied heat on the performance of these devices has also been investigated. In particular, heating asymmetry is found…

► The use of accelerator technology, particularly Graphics Processing Units (GPUs), for scientific computing has increased greatly over the last decade. While this technology allows larger…
(more)

▼ The use of accelerator technology, particularly Graphics Processing Units (GPUs), for scientific computing has increased greatly over the last decade. While this technology allows larger and more complicated problems to be solved faster than before it also presents another opportunity: the real-time and interactive solution of problems. This work aims to investigate the progress that GPU technology has made towards allowing fluid-structure interaction (FSI) problems to be solved in real-time, and to facilitate user interaction with such a solver. A mesoscopic scale fluid flow solver is implemented on third generation nVidia ‘Kepler’ GPUs in two and three dimensions, and its performance studied and compared with existing literature. Following careful optimisation the solvers are found to be at least as efficient as existing work, reaching peak efficiencies of 93% compared with theoretical values. These solvers are then coupled with a novel immersed boundary method, allowing boundaries defined at arbitrary coordinates to interact with the structured fluid domain through a set of singular forces. The limiting factor of the performance of this method is found to be the integration of forces and velocities over the fluid and boundaries; the arbitrary location of boundary markers makes the memory accesses during these integrations largely random, leading to poor utilisation of the available memory bandwidth. In sample cases, the efficiency of the method is found to be as low as 2.7%, although in most scenarios this inefficiency is masked by the fact that the time taken to evolve the fluid flow dominates the overall execution time of the solver. Finally, techniques to visualise the fluid flow in-situ are implemented, and used to allow user interaction with the solvers. Initially this is achieved via keyboard and mouse to control the fluid properties and create boundaries within the fluid, and later by using an image based depth sensor to import real world geometry into the fluid. The work concludes that, for 2D problems, real-time interactive FSI solvers can be implemented on a single laptop-based GPU. In 3D the memory (both size and bandwidth) of the GPU limits the solver to relatively simple cases. Recommendations for future work to allow larger and more complicated test cases to be solved in real-time are then made to complete the work.

▼ Magnetohydrodynamic (MHD) investigations of decaying isotropic turbulence
and rectangular jets (RJ) are carried out. A novel MHD latticeBoltzmann scheme that
combines multiple relaxation time (MRT) parameters for the velocity field with a single
relaxation time (SRT) parameter for the Maxwell?s stress tensor is developed for this
study.
In the MHD homogeneous turbulence studies, the kinetic/magnetic energy and
enstrophy decays, kinetic enstrophy evolution, and vorticity alignment with the strain-rate
tensor are evaluated to assess the key physical MHD turbulence mechanisms. The
magnetic and kinetic energies interact and exchange through the influence of the Lorentz
force work. An initial random fluctuating magnetic field increases the vortex stretching
and forward cascade mechanisms. A strong uniform mean magnetic field increases the
anisotropy of the turbulent flow field and causes inverse cascading.
In the RJ studies, an investigation into the MHD effects on velocity, instability,
and the axis-switching phenomena is performed at various magnetic field strengths and
Magnetic Reynolds Numbers. The magnetic field is found to decelerate the jet core,
inhibit instability, and prevent axis-switching. The key physical mechanisms are: (i) the
exchange of energy between kinetic and magnetic modes and (ii) the magnetic field
effect on the vorticity evolution.
From these studies, it is found that magnetic field influences momentum, vorticity,
and energy evolution and the degree of modification depends on the field strength. This
interaction changes vortex evolution, and alters turbulence processes and rectangular jet
flow characteristics. Overall, this study provides more insight into the physics of MHD
flows, which suggests possible applications of MHD Flow Control.
Advisors/Committee Members: Girimaji, Sharath S. (advisor), Morrison, Gerald (committee member), Richard, Jacques (committee member).

►LatticeBoltzmann Method is evolving as a substitute to the prevalent and predominant CFD modeling especially in cases such as multiphase flows, porous media flows…
(more)

▼LatticeBoltzmann Method is evolving as a substitute
to the prevalent and predominant CFD modeling especially in cases
such as multiphase flows, porous media flows and micro flows. This
study is aimed at developing simulation model for multiphase flows
for practical applications such as cavitation in a journal bearing
or lubrication of micro contact. The code is first validated
against benchmark single phase flows like Poiseulle flow and flow
over a cylinder. In the process, various boundary conditions like
velocity, pressure, out-flow, no-slip and periodic boundary
conditions are tested. Finally, the Shan-Chen model for multiphase
physics, which is based on the interaction force between the fluid
particles, is incorporated into the code and is
validated.
Advisors/Committee Members: Cioc, Sorin (Advisor).

► In this work, a multicomponent latticeBoltzmann model is developed for the simulation of multiphase mixing, reactions, and separations processes. This model is unique in…
(more)

▼ In this work, a multicomponent latticeBoltzmann model is developed for the simulation of multiphase mixing, reactions, and separations processes. This model is unique in that diffusive mass transfer of a component in the model is driven by gradients of chemical potential. This fundamentally correct description of diffusion accurately captures the mass transfer in both single phase and multiple phase cases, making the model very versatile.
To validate the model, analysis was performed at three levels: the component level, the phase level, and the systems level. At the component level, the accuracy of the mass and momentum transfer in the model was determined analytically and verified numerically. At the phase level, the chemical equilibrium and interface behavior in multiphase fluids was analyzed. Finally, at the systems level, the model was used to simulate a multiphase separations device used in the production of biodiesel.
Advisors/Committee Members: Jovanovic, Goran N (advisor), Jovanovic, Goran (committee member).

► This thesis describes the development of a LatticeBoltzmann (LB) model for a binary gas mixture. Specifically, channel flow driven by a density gradient with…
(more)

▼ This thesis describes the development of a LatticeBoltzmann (LB) model for a binary gas mixture. Specifically, channel flow driven by a density gradient with diffusion slip occurring at the wall is studied in depth. The first part of this thesis sets the foundation for the multi-component model used in the subsequent chapters. Commonly used single component LB methods use a non-physical equation of state, in which the relationship between pressure and density varies according to the scaling used. This is fundamentally unsuitable for extension to multi-component systems containing gases of differing molecular masses that are modelled with the ideal gas equation of state. Also, existing methods for implementing boundary conditions are unsuitable for extending to novel boundary conditions, such as diffusion slip. Therefore, a new single component LB derivation and a new method for implementing boundary conditions are developed, and validated against Poiseuille flow. However, including a physical equation of state reduces stability and time accuracy, leading to longer computational times, compared with 'incompressible' LB methods. The new method of analysing LB boundary conditions successfully explains observations from other commonly used schemes, such as the slip velocity associated with 'bounce-back'.The new model developed for multi-component gases avoids the pitfalls of some other LB models, a single computational grid is shared by all the species and the diffusivity is independent of the viscosity. The Navier-Stokes equation for the mixture and the Stefan-Maxwell diffusion equation are both recovered by the model. However, the species momentum equations are not recovered correctly and this can lead to instability. Diffusion slip, the non-zero velocity of a gas mixture at a wall parallel to a concentration gradient, is successfully modelled and validated against a simple one-dimensional model for channel flow. To increase the accuracy of the scheme a second order numerical implementation is needed. This can be achieved using a variable transformation method which does not result in an increase in computational time. Simulations were carried out on hydrogen and water diffusion through a narrow channel, with varying total pressure and concentration gradients. For a given value of the species mass flux ratio, the total pressure gradient was dependent on the species concentration gradients. These results may be applicable to fuel cells where the species mass flux ratio is determined by a chemical reaction and the species have opposing velocities. In this case the total pressure gradient is low and the cross-channel average mass flux of hydrogen is independent of the channel width. Finally, solutions for a binary Stefan tube problem were investigated, in which the boundary at one end of a channel is permeable to hydrogen but not water. The water has no total mass flux along the channel but circulates due to the slip velocity at the wall. The cross-channel average mass flux of the hydrogen along the channel increases…

► This dissertation presents the development of numerical models based on latticeBoltzmann (LB) and cellular automaton (CA) methods for solving phase change and microstructural…
(more)

▼ This dissertation presents the development of numerical models based on latticeBoltzmann (LB) and cellular automaton (CA) methods for solving phase change and
microstructural evolution problems. First, a new variation of the LB method is discussed
for solving the heat conduction problem with phase change. In contrast to previous
explicit algorithms, the latent heat source term is treated implicitly in the energy
equation, avoiding iteration steps and improving the formulation stability and efficiency.
The results showed that the model can deal with phase change problems more accurately
and efficiently than explicit LB models.
Furthermore, a new numerical technique is introduced for simulating dendrite
growth in three dimensions. The LB method is used to calculate the transport phenomena
and the CA is employed to capture the solid/liquid interface. It is assumed that the
dendritic growth is driven by the difference between the local actual and local
equilibrium composition of the liquid in the interface. The evolution of a threedimensional
(3D) dendrite is discussed. In addition, the effect of undercooling and degree
of anisotropy on the kinetics of dendrite growth is studied.
Moreover, effect of melt convection on dendritic solidification is investigated
using 3D simulations. It is shown that convection can change the kinetics of growth by
affecting the solute distribution around the dendrite. The growth features of twodimensional
(2D) and 3D dendrites are compared. Furthermore, the change in growth
kinetics and morphology of Al-Cu dendrites is studied by altering melt undercooling,
alloy composition and inlet flow velocity.
The local-type nature of LB and CA methods enables efficient scaling of the
model in petaflops supercomputers, allowing the simulation of large domains in 3D. The
model capabilities with large scale simulations of dendritic solidification are discussed
and the parallel performance of the algorithm is assessed. Excellent strong scaling up to
thousands of computing cores is obtained across the nodes of a computer cluster, along
with near-perfect weak scaling. Considering the advantages offered by the presented
model, it can be used as a new tool for simulating 3D dendritic solidification under
convection.
Advisors/Committee Members: Dr. Rogelio Luck (committee member), Dr. Mark F. Horstemeyer (committee member), Dr. Sergio D. Felicelli (chair), Dr. Mohsen Asle Zaeem (committee member).

► This thesis describes the development of a LatticeBoltzmann (LB) model for a binary gas mixture. Specifically, channel flow driven by a density gradient with…
(more)

▼ This thesis describes the development of a LatticeBoltzmann (LB) model for a binary gas mixture. Specifically, channel flow driven by a density gradient with diffusion slip occurring at the wall is studied in depth.
The first part of this thesis sets the foundation for the multi-component model used in the subsequent chapters. Commonly used single component LB methods use a non-physical equation of state, in which the relationship between pressure and density varies according to the scaling used. This is fundamentally unsuitable for extension to multi-component systems containing gases of differing molecular masses that are modelled with the ideal gas equation of state. Also, existing methods for implementing boundary conditions are unsuitable for extending to novel boundary conditions, such as diffusion slip. Therefore, a new single component LB derivation and a new method for implementing boundary conditions are developed, and validated against Poiseuille flow. However, including a physical equation of state reduces stability and time accuracy, leading to longer computational times, compared with 'incompressible' LB methods. The new method of analysing LB boundary conditions successfully explains observations from other commonly used schemes, such as the slip velocity associated with 'bounce-back'.
The new model developed for multi-component gases avoids the pitfalls of some other LB models, a single computational grid is shared by all the species and the diffusivity is independent of the viscosity. The Navier-Stokes equation for the mixture and the Stefan-Maxwell diffusion equation are both recovered by the model. However, the species momentum equations are not recovered correctly and this can lead to instability. Diffusion slip, the non-zero velocity of a gas mixture at a wall parallel to a concentration gradient, is successfully modelled and validated against a simple one-dimensional model for channel flow. To increase the accuracy of the scheme a second order numerical implementation is needed. This can be achieved using a variable transformation method which does not result in an increase in computational time.
Simulations were carried out on hydrogen and water diffusion through a narrow channel, with varying total pressure and concentration gradients. For a given value of the species mass flux ratio, the total pressure gradient was dependent on the species concentration gradients. These results may be applicable to fuel cells where the species mass flux ratio is determined by a chemical reaction and the species have opposing velocities. In this case the total pressure gradient is low and the cross-channel average mass flux of hydrogen is independent of the channel width.
Finally, solutions for a binary Stefan tube problem were investigated, in which the boundary at one end of a channel is permeable to hydrogen but not water. The water has no total mass flux along the channel but circulates due to the slip velocity at the wall. The cross-channel average mass flux of the hydrogen along the…

In this thesis, two numerical modeling methods are used to investigate the thermal conductivity of the polymer electrolyte membrane (PEM) fuel cell gas diffusion layer…
(more)

▼

In this thesis, two numerical modeling methods are used to investigate the thermal conductivity of the polymer electrolyte membrane (PEM) fuel cell gas diffusion layer (GDL). First, an analytical model is used to study the through-plane thermal conductivity from representative physical GDL models informed by microscale computed tomography imaging of four commercially available GDL materials. The effect of the heterogeneity of the through-plane porosity of the GDL and polytetrafluoroethylene (PTFE) treatment is studied and it is noted that the high porosity surface transition regions have a dominating effect over the addition of PTFE in impacting the overall thermal conductivity. Next, the latticeBoltzmann method (LBM) is employed to study both the in-plane and through-plane thermal conductivity of stochastic numerically generated GDL modeling domains. The effect of GDL compression, binder content, PTFE treatment, addition of a microporous layer (MPL), heterogeneous porosity distributions, and water saturation on the thermal conductivity are investigated.

► We study the use of latticeBoltzmann (LB) methods for simulation of turbulent fluid flows motivated by their high computational throughput and amenability to highly…
(more)

▼ We study the use of latticeBoltzmann (LB) methods for simulation of turbulent fluid flows motivated by their high computational throughput and amenability to highly parallel platforms such as graphics processing units (GPUs). Several algorithmic improvements are unearthed including work on non-unit Courant numbers, the force operator, use of alternative topologies based on face and body centered cubic lattices and a new formulation using a generalized eigendecomposition that allows a new freedom in tuning the eigenvectors of the linearised collision operator. Applications include a variable bulk viscosity and the use of a stretched grid, our implementation of which reduces errors present in previous efforts. We present details for numerous lattices including all required matrices, their moments the procedures and programs used to generate these and perform linear stability analysis.
Small Mach number flows where density variations are negligible except in the buoyancy force term allow the use of a highly accurate finite volume solver to simulate the evolution of the buoyancy field which is coupled to the LB simulation as an external force. We use a multidimensional flux limited third order flux integral based advection scheme. The simplified algorithm we have devised is easier to implement, has higher performance and does not sacrifice any accuracy compared to the leading alternative. Our algorithm is particularly suited to an outflow based implementation which furthers the stated benefits. We present numerical experiments confirming the third order accuracy of our scheme when applied to multidimensional advection.
The coupled solver is implemented in a new code that runs in parallel across multiple machines using GPUs. Our code achieves high computational throughput and accuracy and is used to simulate a range of turbulent flows. Details regarding turbulent channel flow and sheared convective boundary layer simulations are presented including some new insight into the scaling properties of the latter flow.

► The motion of microorganisms presents interesting and diffcult problems ranging from mechanisms of propulsion to collective effects. Experimentally, some of the complicating factors, such as…
(more)

▼ The motion of microorganisms presents interesting and diffcult problems ranging from mechanisms of propulsion to collective effects. Experimentally, some of the complicating factors, such as death, reproduction, chemotaxis, etc., can be suppressed through genetic manipulation or environmental control. Nonequilibrium statistical mechanics has been used to study simple models, however proceeding analytically is extremely challenging. Thus simulations, where one has total control over and knowledge of the system, are a compelling method for examining models of their behaviour. In this work I present simulations of minimal, self-propelled particles, while ensuring realistic hydrodynamic behaviour using the latticeBoltzmann method (LBM), a well-studied method for simulating fluid flows that scales linearly in computational effort with the system volume. The derivation of the LBM is reviewed, including the addition of forces in a consistent, accurate
manner as well as thermal fluctuations that satisfy the fluctuation-dissipation theorem. It is extended to include singular forces via a regularization of the Dirac δ-function. This is implemented and extensively tested for agreement with low Reynolds number hydrodynamics. The regularized singularities are used to develop an effcient algorithm for pointlike particles which move under the influence of an external force, such as gravity, or thermal fluctuations of the fluid. The method is compared to theoretical results and simulations using a well-studied algorithm that resolves the particle, finding good agreement in the dilute limit and significantly reduced computational requirements. Using the singular forces, we then construct a minimal model for self-propelled particles, that may also experience forces or undergo random changes of orientation (modelling the “run-and-tumble” dynamics observed in swimming bacteria such as E. coli). The collective behaviour of these model swimmers
is studied in three situations: sedimentation under gravity; in a central, harmonic trap; and in a Poiseuille flow between parallel plates. For sedimentation, the behaviour is not very different from that expected of non-interacting run-and-tumble particles, except that total collapse to the container bottomwhen the weight of the particles equals the propelling force is prevented by the velocity fluctuations caused by the particles’ activity. The trapped particles, for runlengths comparable to the trap size, self-assemble into a pump-like structure, while for short run-lengths an approximately Gaussian distribution seenwithout hydrodynamic interactions, is maintained. In Poiseuille flows we find the particles orient upstream; forweak flows this results in a net upstreamcurrent. We find significant hydrodynamic effects, in the dilute limit, only when there is some mechanism that causes alignment of the particles.

► In this work, the latticeBoltzmann method (LBM) was validated for direct numerical simulation (DNS) of wall-bounded turbulent flows. The LBM is a discrete-particle-based method…
(more)

▼ In this work, the latticeBoltzmann method (LBM) was validated for direct numerical simulation (DNS) of wall-bounded turbulent flows. The LBM is a discrete-particle-based method that numerically solves the Boltzmann equation as opposed to conventional DNS methods that are based on the Navier-Stokes (NS) equations. The advantages of the LBM are its simple implementation, its ability to handle complex geometries, and its scalability on modern high-performance computers.
An LBM code was developed and used to simulate fully-developed turbulent channel flow. In order to validate the results, the turbulence statistics were compared to those calculated from a conventional NS-based finite difference (FD) simulation. In the present study, special care was taken to make sure the computational domains for LBM and FD simulations were the same. Similar validation studies in the literature have used LBM simulations with smaller computational domains in order to reduce the computational cost. However, reducing the size of the computational domain affects the turbulence statistics and confounds the results of the validation.
The turbulence statistics calculated from the LBM and FD simulations were found to agree qualitatively; however, there were several significant deviations, particularly in the variance profiles. The largest discrepancy was in the variance of the pressure fluctuations, which differed by approximately 7%. Given that both the LBM and FD simulations resolved the full range of turbulent scales and no models were used, this error was deemed to be significant.
The cause of the discrepancy in the pressure variance was found to be the compressibility of the LBM. The LBM allows the density to vary, while the FD method does not since it solves the incompressible form of the NS equations. The effect of the compressibility could be reduced by lowering the Mach number, but this would come at the cost of significantly increasing the computational cost. Therefore, the conclusion of this work is that, while the LBM is capable of producing accurate solutions for incompressible turbulent flows, it is significantly more expensive than conventional methods for simple wall-bounded turbulent flows.

► The aim of this paper is to present a 2-D computational model of particle-laden flows over staggered fibers at a Reynolds number of 1 by…
(more)

▼ The aim of this paper is to present a 2-D computational model of particle-laden flows over staggered fibers at a Reynolds number of 1 by using a LatticeBoltzmann method. The trajectory of particle motion are described by Lagrangian tracking method with a combination of drag, gravity, Saffman lift force, Brownian forces acting on the particles. This study investigated the effect of packing density and fiber geometry in particle size from 7 nm to 500 nm, the range includes main particle collection mechanisms: Brownian diffusion, interception and inertial impaction. The packing density of fiber ranges from 5.6% to 19.63%. Present results show the correlation between fiber arrangements and particle collection. The fiber geometry adopted in the study includes cylinder, diamond and square. It is found out that among the geometries studied, fibers with diamond shape have higher particle capture efficiency in the interception mechanism dominated cases. We also simulate the particle loading on a single fiber and two attached fibers using a LatticeBoltzmann cellular automata method in Brownian diffusion dominated cases. The simulation results present the patterns of particle deposition and the dendrite structure on fiber surface.
Advisors/Committee Members: Chih-Neng Hsu (chair), Chien-Chou Tseng (chair), Kuang C. Lin (committee member), Sheng-Lun Lin (chair).

► Millions of years of evolution have led to a wealth of highly adapted functional surfaces in nature. Among the most fascinating are superhydrophobic surfaces which…
(more)

▼ Millions of years of evolution have led to a wealth of highly adapted functional surfaces in nature. Among the most fascinating are superhydrophobic surfaces which are highly water-repellent and shed drops very easily owing to their chemical hydrophobicity combined with micropatterning. Superhydrophobic materials have attracted a lot of attention due to their practical applications as ultra-low friction surfaces for ships and pipes, water harvesters, de-humidifiers and cooling systems. At small length scales, where surface tension dominates over gravity, these surfaces show a wealth of phenomena interesting to physicists, such as directional flow, rolling, and drop bouncing. This thesis focuses on two examples of dynamic drop interactions with micropatterned surfaces and studies them by means of a latticeBoltzmann simulation approach. Inspired by recent experiments, we investigate the phenomenon of the self-propelled bouncing of coalescing droplets. On highly hydrophobic patterned surfaces drop coalescence can lead to an out-of-plane jump of the composite drop. We discuss the importance of energy dissipation to the jumping process and identify an anisotropy of the jumping ability with respect to surface features. We show that Gibbs' pinning is the source of this anisotropy and explain how it leads to the inhibition of coalescence-induced jumping. The second example we study is the novel phenomenon of pancake bouncing. Conventionally, a drop falling onto a superhydrophobic surface spreads due to its inertia, retracts due to its surface tension, and bounces off the surface. Here we explain a different pathway to bouncing that has been observed in recent experiments: A drop may spread upon impact, but leave the surface whilst still in an elongated shape. This new behaviour, which occurs transiently for certain impact and surface parameters, is due to reversible liquid imbibition into the superhydrophobic substrate. We develop a theoretical model and test it on data from experiments and simulations. The theoretical model is used to explain pancake bouncing in detail.

The problem of acoustic resonances in a corrugated pipe under flow has been studied both experimentally and numerically. Analyzes concerning the flow structure during the whistling phenomenon are performed. They aim to better understand the nature of the phenomenon and the aeroacoustic coupling involved.Laboratory experiments were carried out on three geometries of corrugated veins of short lengths(1 to 2 m). An air flow was applied for speeds between 10 and 25 m/s and a pressure close toatmospheric pressure showing the longitudinal acoustic resonances. Measurements by hotwires,microphone and laser technique (Particle Image Velocimetry) allowed to characterize the flow under conditions favoring whistling. On these different measures, we applied a spatio-temporal reconstructiontechnique, the Linear…

Two-fluid extensions of LatticeBoltzmann methods with free boundaries usually consider ``microscopic'' pseudopotential interface models. In this paper, we rather propose an interface-capturing LatticeBoltzmann approach where the mass fraction variable is considered as an unknown and is advected. Several works have reported the difficulties of LBM methods to deal with such two-fluid systems especially for high-density ratio configurations. This is due to the mixing nature of LBM, as with Flux vector splitting approaches for Finite Volume methods. We here give another explanation of the lack of numerical diffusion of LatticeBoltzmann approaches to accurately capture contact discontinuities. To fix the problem, we propose an arbitrary Lagrangian-Eulerian (ALE) formulation of Lattice-Boltzmann methods. In the Lagrangian limit, it allows for a proper separated treatment of pressure waves and advection phenomenon. After the ALE solution, a remapping (advection) procedure is necessary to project the variables onto the Eulerian Lattice-Boltzmann grid.We explain how to derive this remapping procedure in order to get second-order accuracy and achieve sharp stable oscillation-free interfaces. It has been shown that mass fractions variables satisfy a local discrete maximum principle and thus stay in the range [0,1]. The theory is supported by numerical computations of rising bubbles (without taking into account surface tension at this current state of development).Even if our methods are currently…

This work aims at developing an adjoint solver in ProLB, the aerodynamic software based on the Lattice-Boltzmann method used by Renault. The adjoint solver makes it possible to calculate the surface sensitivities of the aerodynamic forces acting on an obstacle, such as a vehicle, with respect to its shape. The final purpose is to deform it, using morphing techniques based on a fixed step gradient descent method, in order to reduce its drag. First, the step by step development process of the adjoint solver is shown through 2D laminar test cases. The choice of the drag force expression is important because it has an impact on the complexity of the adjoint equations and on the gradient calculation. It is shown that calculating the drag force in the wake of the obstacle is more adequate than calculating it on the obstacle directly. The aim being to minimize the time-averaged drag force, it is demonstrated that the best trade-off between the gradients accuracy and the computation cost is obtained by time-averaging the unsteady direct field. Then, the study of 3D large-scale turbulent cases shows that the algorithms used for the 2D laminar cases are not stable enough to be used in this more complicated context. Changes have therefore been brought to the adjoint solver, in order to use it in an industrial context. Every assumption used for the development of the adjoint solver…

▼ Computational fluid dynamics (CFD) encompasses a variety of numerical methods. Some depend on macroscopic model representatives, which are solved by finite volume, finite element or finite difference method, while others rely on a microscopic description. The latticeBoltzmann method (LBM) is considered a mesoscopic particle method, with its scale lying between macroscopic and microscopic. LBM works well when solving incompressible flow problems, but limitations arise when solving compressible flows, particularly at high Mach numbers. In the present research, this limitation will be overcome by using higher-order Taylor series expansion of the Maxwell equilibrium distribution function and Kataoka and Tsutahara (KT) models for compressible flows. The multiple relaxation times (MRT) approach associated with the collision term of the latticeBoltzmann equation (LBE) will be adopted to enhance the numerical stability of the code, while the large eddy simulation (LES) scale model will be implemented in LBM to simulate compressible jet flows at high subsonic speeds pertinent to jet noise problems. Three-dimensional simulation is performed using 19- and 15-lattice velocity with D3Q19 and D3Q15 models, respectively. In addition, compressible LBM is applied to simulate both heated and unheated jets to show the ability of the nonadiabatic fifth-order equilibrium distribution function in solving nonadiabatic compressible flows. The near-field flow physics and noise simulations are performed using a compressible latticeBoltzmann method. The results from the LMB simulation are used in the Kirchhoff surface integral approach to predict far-field jet noise. Finally, because of the ability of latticeBoltzmann in parallel computing and to improve the computation efficiency of LBM on the numerical simulations of turbulent flows, compute unified device architecture (CUDA) is used to implement LBM in the graphics processing unit (GPU), creating the hybrid code LBM-MRT-LES by utilizing the Kirchhoff integral method, a powerful tool for simulating aeroacoustics problems.

► The topic of this thesis is the numerical study and implementation of the LBM using D2Q9-model for Multiple Relaxation Time (MRT), this model was applied…
(more)

▼ The topic of this thesis is the numerical study and implementation of the LBM using D2Q9-model for Multiple
Relaxation Time (MRT), this model was applied for the fluid flow, temperature and concentration field . A code was
developed using an open-source LBM code and modified for the purpose to simulate the heat and mass transfer
process. This thesis is divided in two parts. (I) Study of the laminar flow in a pipe and channel were simulate
(Hagen-Poiseuille flow), as well as a Lid-driven cavity for a incompressible laminar flow and convection-diffusion
problem of a Gaussian pulse was executed , for a heat and mass transfer, natural convection in a closed cavity and
mass flux rate in a plate were performed with the objective to analyze the boundary condition of LBM for passive
scalar concentration. (II) The main objective was the study of the steady and unsteady laminar flow in a channel with
open square cavity and heated bottom wall. The Boussinesq approximation equation were applied, and it obtained a
good accuracy and stability. LBM was compared against results obtained by ANSY-Fluent software for validation.
Temperature, velocity and Nusselt number, calculated with TLBM presented very well agreement for the set of
Reynolds and Richardson numbers studied.
Advisors/Committee Members: [email protected] (authoremail), false (authoremailshow), Cuesta Romeo, Ildefonso (director), Salueña Pérez, Clara (codirector), true (authorsendemail).

► Blood rheology (haemorheology) plays a key role in tissue perfusion and its alteration from physiological conditions is often the main cause of cardiovascular pathologies. Therefore,…
(more)

▼ Blood rheology (haemorheology) plays a key role in tissue perfusion and its alteration from physiological conditions is often the main cause of cardiovascular pathologies. Therefore, the study of blood velocity profiles and wall shear stress distribution along micro-vessels is important in the field of cardiovascular diseases research. Recent advances in organ-on-a-chip highlighted the possibility of using artificial lung-on-chips which have been developed to replace the respiratory functions of the human lungs in pharmaceutical tests. We have expanded the study of micro-separation processes through micro-porous membranes by developing a numerical tool able to model the behavior of lung-on-a-chip micro-devices in both two and three dimensional geometries. As this is a multiscale problem, the new code consists in a hybrid LBM-FD (LatticeBoltzmann - finite difference) model on a non-uniform material grid, that models mass transfer processes in non-Newtonian flows. A part from the validation of the code, results obtained include the correlations of the non-dimensional numbers involved in mass transfer processes and the dependence on porosity, and the study of concentration profiles under steady (pipe flow) and the beginning of the study in non-steady (Womersley flow) conditions.
The LBM-FD hybrid model was used to study the mass transport through a hydrophobic micro-porous membrane located in-between a co-current flow passing through rectangular channels, which is similar to the micro-device used in Lung-On-a-Chip research. This code has been used to perform a parametric study to find the empirical correlation between Peclet number in the permeate channel and the mass transfer processes across the membrane which is quantified by mean of Sherwood number. The correlations in the two-dimensional micro-device reproduce correctly the linear scaling law of <Sh> with the number of pores. The correlations give a power value equal to 1/3 (which characteristic of the Graetz-Leveque problem) for the scaling exponent of the average Sherwood number with Pe. This has been done in 2D and 3D models. In the three-dimensional case, we compared the results obtained using the power-law flow with a shear-thinning degree of n=0.7 against the results obtained using the Newtonian hypothesis (n=1). The non-Newtonian case.
Advisors/Committee Members: [email protected] (authoremail), true (authoremailshow), Salueña Pérez, Clara (director), Vernet Peña, Anton (director), Cito, Salvatore (director), true (authorsendemail).

► This thesis is concerned with the new formulation of a finite-volume latticeBoltzmann equation method and its implementation on unstructured meshes. The finite-volume discretization with…
(more)

▼ This thesis is concerned with the new formulation of a finite-volume latticeBoltzmann equation method and its implementation on unstructured meshes. The finite-volume discretization with a cell-centered tessellation is employed. The new formulation effectively adopts a total variation diminishing concept. The formulation is analyzed for the modified partial differential equation and the apparent viscosity of the model. Further, the high-order extension of the present formulation is laid out. Parallel simulations of a variety of two-dimensional benchmark flows are carried out to validate the formulation.
In Chapter 1, the important notions of the kinetic theory and the most celebrated equation in the kinetic theory, ‘the Boltzmann equation’ are given. The historical developments and the theory of a discrete form of Boltzmann equation are briefly discussed. Various off-lattice schemes are introduced. Various methodologies adopted in the past for the solution of the latticeBoltzmann equation on finite-volume discretization are reviewed. The basic objectives of this thesis are stated.
In Chapter2,the basic formulations of latticeBoltzmann equation method with a rational behind different boundary condition implementations are discussed. The benchmark flows are studied for various flow phenomenon with the parallel code developed in-house. In particular, the new benchmark solution is given for the flow induced inside a rectangular, deep cavity.
In Chapter 3, the need for off-lattice schemes and a general introduction to the finite-volume approach and unstructured mesh technology are given. A new mathematical formulation of the off-lattice finite-volume latticeBoltzmann equation procedure on a cell-centered, arbitrary triangular tessellation is laid out. This formulation employs the total variation diminishing procedure to treat the advection terms. The implementation of the boundary condition is given with an outline of the numerical implementation. The Chapman-Enskog (CE) expansion is performed to derive the conservation equations and an expression for the apparent viscosity from the finite-volume latticeBoltzmann equation formulation in Chapter 4. Further, the numerical investigations are performed to analyze the apparent viscosity variation with respect to the grid resolution.
In Chapter 5, an extensive validation of the newly formulated finite-volume scheme is presented. The benchmark flows considered are of increasing complexity and are namely
(1) Posieuille flow, (2) unsteady Couette flow, (3) lid-driven cavity flow, (4) flow past a backward step and (5) steady flow past a circular cylinder. Further, a sensitivity study to the various limiter functions has also been carried out.
The main objective of Chapter6is to enhance the order of accuracy of spatio-temporal calculations in the newly presented finite-volume latticeBoltzmann equation formulation. Further, efficient implementation of the formulation for parallel processing is carried out. An appropriate decomposition of the computational domain is…
Advisors/Committee Members: Lakshmisha, K N.

Vilasrao, P. D. (2010). Development Of A New Finite-Volume Lattice Boltzmann Formulation And Studies On Benchmark Flows. (Thesis). Indian Institute of Science. Retrieved from http://hdl.handle.net/2005/1250

Note: this citation may be lacking information needed for this citation format:Not specified: Masters Thesis or Doctoral Dissertation

Vilasrao PD. Development Of A New Finite-Volume Lattice Boltzmann Formulation And Studies On Benchmark Flows. [Internet] [Thesis]. Indian Institute of Science; 2010. [cited 2020 Jun 07].
Available from: http://hdl.handle.net/2005/1250.

Note: this citation may be lacking information needed for this citation format:Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Vilasrao PD. Development Of A New Finite-Volume Lattice Boltzmann Formulation And Studies On Benchmark Flows. [Thesis]. Indian Institute of Science; 2010. Available from: http://hdl.handle.net/2005/1250

Note: this citation may be lacking information needed for this citation format:Not specified: Masters Thesis or Doctoral Dissertation

Indian Institute of Science

26.
Vilasrao, Patil Dhiraj.
Development Of A New Finite-Volume LatticeBoltzmann Formulation And Studies On Benchmark Flows.

► This thesis is concerned with the new formulation of a finite-volume latticeBoltzmann equation method and its implementation on unstructured meshes. The finite-volume discretization with…
(more)

▼ This thesis is concerned with the new formulation of a finite-volume latticeBoltzmann equation method and its implementation on unstructured meshes. The finite-volume discretization with a cell-centered tessellation is employed. The new formulation effectively adopts a total variation diminishing concept. The formulation is analyzed for the modified partial differential equation and the apparent viscosity of the model. Further, the high-order extension of the present formulation is laid out. Parallel simulations of a variety of two-dimensional benchmark flows are carried out to validate the formulation.
In Chapter 1, the important notions of the kinetic theory and the most celebrated equation in the kinetic theory, ‘the Boltzmann equation’ are given. The historical developments and the theory of a discrete form of Boltzmann equation are briefly discussed. Various off-lattice schemes are introduced. Various methodologies adopted in the past for the solution of the latticeBoltzmann equation on finite-volume discretization are reviewed. The basic objectives of this thesis are stated.
In Chapter2,the basic formulations of latticeBoltzmann equation method with a rational behind different boundary condition implementations are discussed. The benchmark flows are studied for various flow phenomenon with the parallel code developed in-house. In particular, the new benchmark solution is given for the flow induced inside a rectangular, deep cavity.
In Chapter 3, the need for off-lattice schemes and a general introduction to the finite-volume approach and unstructured mesh technology are given. A new mathematical formulation of the off-lattice finite-volume latticeBoltzmann equation procedure on a cell-centered, arbitrary triangular tessellation is laid out. This formulation employs the total variation diminishing procedure to treat the advection terms. The implementation of the boundary condition is given with an outline of the numerical implementation. The Chapman-Enskog (CE) expansion is performed to derive the conservation equations and an expression for the apparent viscosity from the finite-volume latticeBoltzmann equation formulation in Chapter 4. Further, the numerical investigations are performed to analyze the apparent viscosity variation with respect to the grid resolution.
In Chapter 5, an extensive validation of the newly formulated finite-volume scheme is presented. The benchmark flows considered are of increasing complexity and are namely
(1) Posieuille flow, (2) unsteady Couette flow, (3) lid-driven cavity flow, (4) flow past a backward step and (5) steady flow past a circular cylinder. Further, a sensitivity study to the various limiter functions has also been carried out.
The main objective of Chapter6is to enhance the order of accuracy of spatio-temporal calculations in the newly presented finite-volume latticeBoltzmann equation formulation. Further, efficient implementation of the formulation for parallel processing is carried out. An appropriate decomposition of the computational domain is…
Advisors/Committee Members: Lakshmisha, K N.

Vilasrao, P. D. (2010). Development Of A New Finite-Volume Lattice Boltzmann Formulation And Studies On Benchmark Flows. (Thesis). Indian Institute of Science. Retrieved from http://etd.iisc.ernet.in/handle/2005/1250 ; http://etd.ncsi.iisc.ernet.in/abstracts/1629/G23819-Abs.pdf

Note: this citation may be lacking information needed for this citation format:Not specified: Masters Thesis or Doctoral Dissertation

Note: this citation may be lacking information needed for this citation format:Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Vilasrao PD. Development Of A New Finite-Volume Lattice Boltzmann Formulation And Studies On Benchmark Flows. [Thesis]. Indian Institute of Science; 2010. Available from: http://etd.iisc.ernet.in/handle/2005/1250 ; http://etd.ncsi.iisc.ernet.in/abstracts/1629/G23819-Abs.pdf

Note: this citation may be lacking information needed for this citation format:Not specified: Masters Thesis or Doctoral Dissertation

► Interactions between droplets were studied using two latticeBoltzmann methods (LBMs). The Shan-Chen LBM, in which repulsive forces between fluids maintain phase separation, was used…
(more)

▼ Interactions between droplets were studied using two
latticeBoltzmann methods (LBMs). The Shan-Chen LBM, in which
repulsive forces between fluids maintain phase separation, was used
to simulate systems with three immiscible components. The
simulations demonstrated the three equilibrium configurations of
two droplets in a third fluid: adhering, separated, and engulfed.
Simulations of adhering droplet pairs, called Janus droplets due to
their two-sided structure, in shear flow revealed the structure of
the internal flow and the dependence of the rotation rate on the
orientation of the droplet. A second type of interaction between
droplets was simulated with the free-energy binary-liquid LBM:
binary droplet collisions in confined simple shear flow. The
conditions for coalescence were quantified and the effects of
geometry and the parameters of this Cahn-Hilliard-type phase field
model on the critical conditions were examined. Two parameters of
the phase field model, the thickness of the diffuse interface and
the mobility of the phase field, are important. Simulations with
highly-resolved droplets, with radii spanning 200 lattice nodes,
were used to determine the minimum film thickness before
coalescence, its relationship to the interface thickness, and the
effect of the mobility on the evolution of the minimum distance
between the droplet interfaces during collisions. The critical
conditions for coalescence in these simulations were compared with
published experiments with polymers. Unlike the experimental
polymer system, the interfaces of interacting droplets are often
charged, as in the case of oil-water emulsions. To simulate such
liquid systems, the free-energy binary-liquid LBM was coupled with
an iterative finite difference solver for the linearized
Poisson-Boltzmann equation that describes the electrostatic
potential near a charged surface in an electrolyte solution.
Simulations of collisions between charged droplets with constant
zeta potentials in a sheared electrolyte showed the effects of
surface charge on the critical conditions for
coalescence.

Flow and transport modeling through porous media is of primary concern nowadays, especially in order to progress in the understanding of pollutant transfers through soils. Soils present frequently heterogeneities such as macropores (caused by…

The latticeBoltzmann method (LBM) have been applied very successfully to hydrodynamic flows in porous media. However, the limitation of these methods to isothermal and hydrodynamic flows, make them inadequate to simulate gas flows in micro-porous media. Indeed, in these conditions, the mean free path of the molecules could be of the same magnitude order as the pore size in which gas flows. Such flows will not be in hydrodynamic regime, but in regimes qualified of, slip or transitional ; for which the LBM are no longer valid. On the other hand, the isothermal character of LBM make them unusable, for example, in the case where the gas undergoes expansion through the media. It is then necessary, to take the kinetic point of view to describe such flows and phenomena. The proposed approach is based on the decomposition of the distribution function on the Hermite polynomials basis and the use of Gauss-Hermite quadrature associated with this projection. The systematic nature of this development naturally leads to consider different order of approximation of the Boltzmann-BGK equation in various quadratures. It then follows from these various approximations, a family of discretizations of the Boltzmann-BGK equation, whose classical LBM are a member. Determining the most suitable approximation is achieved by systematic analysis of the results obtained with different approximation orders.…

This thesis is dedicated to the derivation and the validation of a new collision model as a stabilization technique for high-order latticeBoltzmann methods (LBM). More specifically, it intends to stabilize simulations of: (1) isothermal and weakly compressible flows at high Reynolds numbers, and (2) fully compressible flows including discontinuities such as shock waves. The new collision model relies on an enhanced regularization step. The latter includes a recursive computation of nonequilibrium Hermite polynomial coefficients. These recursive formulas directly derive from the Chapman-Enskog expansion, and allow to properly filter out second- (and higher-) order nonhydrodynamic contributions in underresolved conditions. This approach is even more interesting since it is compatible with a very large number of velocity sets. This high-order LBM is first validated in the isothermal case, and for high-Reynolds number flows. The coupling with a shock-capturing technique allows to further extend its validity domain to the simulation of fully compressible flows including shockwaves. The present work ends with the linear stability analysis(LSA) of the new approach, in the isothermal case. This leads to a proper quantification of the impact induced by each discretization (velocity and numerical) on the spectral properties of the related set of equations. The LSA of the recursive regularized LBM finally confirms the drastic stability gain obtained with this new…